MIS polymeric structures and OTFTs using PMMA on P3HT layers

In this paper we present a detailed characterization of metal–isolator–semiconductor MIS structures and organic thin film transistors (OTFTs) using poly(methyl methacrylate) (PMMA) as gate dielectric on top of a semiconductor poly(3-hexylthiophene) (P3HT) layer. The PMMA layer was spin coated from a 6% dilution of PMMA in anisole. The P3HT layer was spin coated from a 0.66 wt% dilution of P3HT in chloroform. OTFTs with upper gate were fabricated using photolithographic processes. The current density across the dielectric is below 1 × 10−6 A/cm2. The interface states density is below 1 × 1011 cm−2, while the flat band voltage shift is less than 0.5 V for bias stress in the range of ±20 V. Accumulation occurs for gate voltage below −10 V, allowing OTFTs to work in the voltage range below −30 V, with threshold voltage around −2.5 V. Mobility was 2.5 × 10−3 cm2/V s, which is among highest values reported for P3HT OTFTs working in this voltage range.